Bank customers face further chaos today as NatWest has extended its opening
hours once again to cope with the fallout from a computer failure almost a
week ago.

Yesterday around 1,200 branches opened for the first time on a Sunday as staff battled to deal with a backlog of payments following Tuesday's IT glitch.

The debacle rolled into a seventh day today after parent company RBS said it was still experiencing technical issues and admitted some online services were unavailable.

The fiasco – also affecting RBS and Ulster Bank – continued to spark anger this morning with customers apparently unable to access internet banking. During the past week, clients have seen payments to go awry, holiday and home purchases interrupted and wages have appeared to go missing.

Susan Allen, RBS group spokesperson said the bank's "primary focus" was fixing the issues

NatWest has more than 7.5 million personal banking customers but it remains unclear how many have been affected. More than 1,000 NatWest branches were opening their doors from 8am to 7pm today as staff seek to resolve the problems.

Susan Allen, director of customer services at RBS Group, insisted that progress was being made and expressed cautious optimism that RBS and NatWest customer account balances would be largely "back to normal" at the start of the working week.

"The knock-on effects of this technical failure mean there will be bumps in the road," she said. "We will do everything we can to minimise further disruption to our customers."

But clients continued to voice their frustration on the NatWest website this morning. Chris Latimer, from Liverpool, wrote: "wow first time since the glitch, i cant access online banking. this is not good." Another posting, by Jean from Brighton, asked: "why can I not log into online banking to check my balance?"

Others said they had "lost faith" in the bank and complained wages failed to arrive in their accounts. Social media websites have also been awash with criticism from people who found themselves without access to cash over the weekend or unable to pay bills.

Stephen Hester, chief executive of NatWest owner RBS, has issued a public apology for the chaos and conceded the bank had let down its customers. His attempt to reassure clients followed mounting fears that thousands of people could be hit with penalty charges if their regular payments – including mortgages – were affected.

"I am very sorry for the difficulties people are experiencing," he said. "Our customers rely on us day in and day out to get things right, and on this occasion we have let them down. This should not have happened."

The computer software problem started on Tuesday night and reportedly arose following an attempt to install a software update on RBS's payment processing system, which was then corrupted. The group has said this issue has now been fixed.

It has promised that any overdraft fees or charges on current accounts incurred by customers would be automatically waived and has said it would work directly with credit agencies to ensure no one's credit score was affected.

It will also reimburse customers who had to pay to ring an 0845 helpline number for any cost incurred when doing so.